And Now, Amber Waves of ... Concrete?

Here's food for thought: Those good-for-you grains that now stoke your morning cereal may soon also fortify your local dam, highway and bridge.

Engineers in America's heartland are cooking up a new recipe for concrete—the world's most common building material—using post-harvest leftovers from rice, corn and wheat.

The mix is being developed at Kansas State University, where civil engineers are aiming to increase the strength of concrete while reducing its carbon footprint (and finding a use for a lot of agricultural waste in the bargain).

geograph.org.uk

Ash from wheat straw and other agricultural residue replaced 20 percent of the cement in one concrete sample and made it 32 percent stronger, researchers said.

With byproducts of biofuels made from corn stover, wheat straw and rice straw, the researchers are hoping to replace some of the portland cement used in making nearly 7 billion cubic meters of concrete each year.

"Even though making concrete is less energy-intensive than making steel or other building materials, we use so much of it that concrete production accounts for between 3 to 8 percent of global carbon dioxide emissions," Kyle Riding, assistant professor of civil engineering, said in a research announcement.

Wood Chips and Wheat Straw

Feraidon Ataie, a doctoral student in civil engineering, is leading the research.

"The idea is to use bioethanol production byproducts to produce a material to use in concrete as a partial replacement of cement," said Ataie.

His team is specifically looking at byproducts from production of cellulosic ethanol, which is biofuel produced from inedible material such as wood chips, wheat straw or other agricultural residue.

Kansas State University

"By using these materials we can reduce the carbon footprint of concrete materials," says Feraidon Ataie, whose research has gained funding and attention.

Cellulosic ethanol is different from traditional bioethanol, which uses corn and grain to make biofuel. Corn ethanol's byproduct (called distiller's dried grain) can be used as cattle feed, but cellulosic ethanol's byproduct (called high-lignin residue) is often perceived as less valuable.

Strength from Ashes

"With the cellulosic ethanol process, you have leftover material that has lignin and some cellulose in it, but it's not really a feed material anymore," Riding said. "Your choices of how to use it are a lot lower. The most common choices would be to either burn it for electricity or dispose of the ash."

When the researchers added the high-lignin ash byproduct to cement, the ash reacted chemically with the cement to make it stronger. Testing the finished concrete material, the researchers found that replacing 20 percent of the cement with cellulosic material after burning increased the strength of the concrete by 32 percent.

The team has been experimenting with "biofuel pretreatments" to see if they can improve on their ashy mix, Riding said.

From Waste to Asset

Repurposing agricultural waste for use in concrete would be a win-win for both the construction and agricultural industries, researchers say.

Iowa State University

Corn stover—the stalks, leaves and cobs that remain in fields after the harvest—is the largest quantity of biomass residue in the United States.

Kansas and other agricultural states that produce crops such as wheat and corn could use the straw and stover left after harvesting for making cellulosic ethanol.

There is a lot of ag waste to go around. Kansas is the U.S.'s biggest wheat-producing state, and each acre of wheat crop yields about 1.5 tons of wheat straw, according to the University of Wisconsin. Kansas is also a top corn producer, and corn stover (stalks, leaves and cobs that remain in fields after the corn harvest) is the largest quantity of biomass residue in the United States.

Around 120 million tons of biomass residue is available annually, according to the University of Iowa.

"It is predicted that bioethanol production will increase in the future because of sustainability," Ataie said. "As bioethanol production increases, the amount of the byproduct produced also increases. This byproduct can be used in concrete."

Riding said the development "has the potential to make biofuel manufacture more cost effective by better using all of the resources that are being wasted and getting value from otherwise-wasteful material and leftover materials. It has the potential to improve the strength and durability of concrete. It benefits both industries."

Myrabella / Wikimedia Commons

Lafarge (pictured) and other companies make cement and aggregates used in 7 billion cubic meters of concrete each year. Concrete production accounts for 3 to 8 percent of global carbon dioxide emissions, Kansas researchers say.

Funding and Publications

Funded in part by a $210,000 grant from the National Science Foundation, the research has included representatives from the University of Texas, North Carolina State University, and the National Renewable Energy Laboratory in Golden, CO.

Some of the work has been published in the American Society of Civil Engineers' Journal of Materials in Civil Engineering.

"If you use this in concrete to increase strength and quality, then you add value to this byproduct rather than just landfilling it," said Ataie. "If you add value to this byproduct, then it is a positive factor for the industry."

Would this high lignin ash take the place of fly ash currently used in concrete mix designs for the same purpose? And if so, is the environment better off with more unused high lignin ash laying around, or unused fly ash?

Comment from Jerry Trevino, (4/30/2013, 10:12 AM)

It would be interesting to see if this ash and additive to concrete to make it stronger, a replacement of C or F fly ash, or totally new type of pozzolan. With coal plants being shut down by this administration, maybe it would help keep the availability of raw materials up. It would also be interesting to see the material specs, affect on water to cement ratio requirements, etc.

Comment from Tom Schwerdt, (5/1/2013, 8:29 AM)

John, with the rise of natural gas and reduced usage of high-ash coal around here - the concrete guys have been getting worried about fly ash supplies, particularly in areas with ASR concerns due to local aggregates available.

Comment from John Fauth, (5/1/2013, 8:47 AM)

Wow, I'm a few years removed from contact with the coal mining and power generation business, and evidently things have changed. No doubt low cost natural gas has had an impact on both, but I wouldn't have guessed there to be concern over fly ash availability.

Comment from Tom Schwerdt, (5/2/2013, 9:30 AM)

It's also the type of fly ash available - they need Class F fly ash for ASR mitigation. I don't know of anyone who prefers Class C, and Class C just doesn't work for some applications. And shipping fly ash long distances gets cost-prohibitive. I'm not sure they're actually having issues yet, but I'm hearing concerns voiced. Repeatedly. Anyway, the power generation mix has been shifting pretty rapidly for a business where individual plants are typically expecting a lifespan of 30-50 years.